Peel the bananas and mash in a large bowl, leaving a few small pieces for texture. You should have about 1¼ cups mashed banana.

In a separate bowl, whisk together the flour, baking powder, cinnamon and salt.

Stir the brown sugar, egg, milk and vanilla into the mashed bananas until combined. Fold in the flour mixture just until no dry streaks remain. The batter should be thick and scoopable; do not overmix.

Pour enough neutral oil into a small, heavy-bottomed saucepan to reach roughly 1 inch (2.5 cm) deep, keeping the pan less than half full. Heat to 350°F (175°C). Let the batter stand for about 5 minutes while the oil heats.

Carefully lower heaping 2-tablespoon portions of batter into the oil, 3–4 at a time without crowding. Fry for 3–4 minutes total, turning halfway, until deeply golden on all sides. Keep the oil near 340–360°F (170–182°C).

Lift the fritters out with a slotted spoon and drain on a wire rack or paper towels. Break open the first fritter to check that the center is fluffy and fully cooked, not wet or doughy. Adjust portion size or frying time if needed.

Repeat with remaining batter, allowing the oil to return to temperature between batches. You should get about 18 fritters.

Dust with powdered sugar, if using, and serve warm. One serving is approximately 3 fritters.